Laser beam machining devices for so-called axial ring welding or ring hardening are described in German Patent No. DE 10 254 847 and European Patent No. EP 1 508 397. The known laser beam machining devices are characterized in that an annular laser focus lying in a plane is producible with the aid of special optics.
In addition, laser beam machining devices for so-called peripheral ring welding or ring annealing exist, a laser focus extending along the circumference of at least one workpiece being producible using these laser beam machining devices. In particular in laser beam machining devices for producing a peripheral laser focus, adjusting the focal position is problematic, in particular because depending on the design of the laser beam machining device, the laser focus is not externally visible on the at least one workpiece, in particular on the joining point in the contact area of two workpieces. However, in order not to negatively influence the laser beam machining process, it must be ensured that the workpiece to be machined is positioned exactly at the laser focus and does not have any angular error. In the event of inexact positioning, an uneven intensity distribution of the laser focus results, which has a disadvantageous effect on the laser beam machining process and the machining result.